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CREATE A CUSTOM GEARBOX
Imperial (inch) lathe
Metric (mm) lathe
Enter the leadscrew Pitch in mm or Threads Per Inch (TPI)
Automatic Compound Gears
Some modern lathes allow and Chinese mini-lathes allow you to combine any two change gears and use them as compound gears. In that case you can select Automatic mode and the program automatically pairs the gears in every possible way to make up compound gears.
However, some lathes use compound gears with a larger hole in the center than the change gears and you cannot use change gears for compound ratios.
This is the case with Boxford lathes and you should say NO Automatic.
It is possible to make an adapter to solve this problem
and the help file contains photos and drawings showing you how to make it.
Look for a help button (?) labelled "Adapter"
Copy numbers from a row
Find a suitable row in your thread cutting chart and copy it into this input box in increasing order. Use numbers separated by commas.
These represent pitch or TPI on the table.
If you have turned off lengthy instructions it is recommended that you go to the main menu, Preferences, and turn them all on when you use Custom Gearbox for the first time. Otherwise use the help buttons.
The examples shown here define my Boxford Model A lathe. If you want to see how the program operates, cut and paste these examples and enter "imperial" with leadscrew 8 above. Enter numbers without units eg 8 instead of 8TPI or 3mm.
I usually choose the row and column containing the pitch (or TPI) of the leadscrew so that this number appears in both the row and column. However, some lathes do not list the leadscrew pitch in the table. Each lever position requires two entries, one is merely a symbol used to identify the position of the lever and you can use any symbol, and in any order.
The second set of entries are the actual values required to calculate the gear ratios and these are always numbers which should be entered in increasing order. They are actually the pitch or TPI values from the table.
Most thread cutting tables have columns determined by the position of a lever marked with numbers eg. positions 1 to 8.
Usually the row position is determined by the position of a lever marked with letters or "symbols". eg. A,B,C,D and the threads usually increase in multiples of two eg 4,8,16,32 when you look down a column. When you enter these numerical values they should be in increasing order. However the letters may be in reverse order if necessary.
If your table has extra rows which require a different stud gear or leadscrew gear, please ignore these rows in your table. All entries in the table must have the same gear train. It will be necessary to enter the number of teeth on the stud and leadscrew gears later.
If your lathe doesn't fit this exact pattern you can usually make up a similar system that works for you. eg if your lathe has 3 levers you can assign one lever with positions A, B, C and the second lever D, E, F and then combine the settings of two levers eg AE BF etc used in place of single letter symbols. This can be seen in the Boxford X10 lathe which has been listed already. This does get complicated because you have to work out the gear ratios for each letter combination eg AE and BF.
What if your lathe does not have a numbered lever?
If it has a lever with letters instead of numbers you can simply replace the list of number symbols with a list of letters. If your lathe has a simple gearbox with only one lever you can eliminate the number lever by pretending that it has only one position with a value of 1. Its symbol can be left as a blank space. Similarly you can eliminate the letter lever if necessary.
There is a lot of flexibility in this system to accommodate any lever arrangement and even dials which can be seen in the WARD lathe found in the 'Choose Lathe' list. In that case the symbols for positions were defined as 3 O'Clock, 6 O'Clock etc. If you need help, contact the author of the program. Contact details are shown just below the gold logo on the main menu.
Labels for the columns
Enter the labels assigned to the columns as you move across a row. eg 1,2,3,4,5,6,7,8
If you look across a row, each entry in the table is in a different column. Each column has its own heading or label, usually in the top row. Enter them here, separated by commas. These are merely labels or symbols representing each position of the lever. Sometimes the number levers may be labeled in reverse order so that the numbers decrease as the thread pitch increases,
ie 8, 7, 6, 5, 4, 3, 2, 1
They may even use different symbols
eg U, V, X, Y, Z
or combinations described above: AY1, BZ2.
Copy numbers from a column
Copy a column from your thread cutting chart into this input box. Use numbers separated by commas in increasing order. eg 8, 16, 32, 64, 128
These threads usually increase in multiples of two
eg 0.5, 1,2,4,8,16,32,64 when you look down a column.
Although the correct entry here for the Boxford lathe was 8, 16, 32, 64, 128 the computer program divides them by the leadscrew pitch of 8 TPI as explained later. (You may see 1, 2, 4, 8, 16 shown in the table at the end of the results. This "normalized" version should result in a table with actual thread pitches or TPI, like the table you started with.)
Labels for the rows
Enter the labels to assign to the Rows making up this column.
eg A, B, C, D, E
In most cases the rows are labeled with letters of the alphabet. If you look down a column you will notice that you have just entered the values from this column, and that each entry is on a different row. These rows have been assigned some kind of symbol, a number or letter or even pairs of letters. Enter these symbols in the same order as the column in the table. In some cases they may be in reverse alphabetical order. Numbers or letters must be separated by commas, and the number of labels must match the number of positions that you entered in the previous step.
eg A, B, C, D, E
For testing you can copy and paste these example strings.
How Many Compound Gears?
How many compound gears can be included in the gear train (0,1,2)?
This entry is not critical. It is used to set the default value when the lathe is selected for the first time. Compound gears have two gear wheels connected together by a key or rivet. These compound gears do affect the gear ratio of the gear train, but idler wheels, which are just a single gear, do not affect the gear ratio. A large number of gears in the gear train, with a large collection of gears to choose from, can produce a very large number of results, especially when combined with a large acceptable error, or use of the automatic compound gear mode. Automatic mode works out every possible combination of two gears from your set to make up compound pairs.
No Compound Gears
Most lathes generally use no compound gears, unless you are converting between metric and imperial threads, but compound gears do increase the range of threads you can produce.
One Compound Pair
Many lathes use one special compound pair of gear wheels for special purposes such as metric / imperial conversion, but they can be useful for making a special thread. Setting this to one compound as the default is a good idea. A compound gear consists of two gear wheels connected together, plus the stud gear and leadscrew gear making a total of 4 gears in most cases.
Two Compound pairs
Asian lathes may use up to 2 compound gears, but the stud gear cannot be changed and a full gearbox is not provided in most cases. In conventional lathes where stud and LSG are combined with two compound gears there are 6 gears. This gets complicated and can produce thousands of results, especially if a gearbox is included.
Enter the standard list of Change Gears
Enter the number of teeth on each gear in your collection, separated by commas. If you have two gears with the same number of teeth, enter the number twice.
Enter the List of Compound Gears
Skip this if you selected Automatic Compound Gears.
It is not really important because the user can edit the list and enter their own gears. Idler gears should be completely ignored . If you have a compound pair permanently connected together, enter the numbers of teeth with a slash between eg 127/100. But if you have single gears that can be compounded in pairs enter the two individual gears separated by commas.
Does your lathe have power feed to drive the carriage or cross slide. If you know what these gear ratios are, enter them here, otherwise enter 1.0. The apron usually has gears to slow down the power drive, so that it is a fraction of the speed you would have if it was driven directly from the leadscrew.
Power cross-slide gear ratio
Power feed on the cross-slide as a fraction of thread pitch (used for 'facing' or 'surfacing') eg 0.1
(It is 0.3 of carriage feed (0.34) and 0.3 x 0.34 = ~ 0.1)
Power carriage feed gear ratio
Power feed moving the carriage along the length of the bed as a fraction of thread pitch (sometimes known as sliding). eg 0.34
To help identify this lathe in future, can you provide make, model and year?
eg Model_A No Spaces. _imperial or _metric is added later.
Standard Stud Gear
Enter the number of teeth on the stud gear eg 20.
The main part of the thread cutting table is set up with certain standard stud gear and leadscrew gears. Most Western lathes use an idler gear btween the stud gear and leadscrew gear, and this does not affect the gear ratio. If compound gears have been entered in the 'Chinese' section below, they are included in the gear train to calculate the gear train gear ratio (stdGTR) which is then used to calculate the primary Ratio (pR) of the gearbox. Once pR has been calculated, the standard gears are no longer required. e.g. For the Boxford A lathe the stud gear should be 20.
Standard Leadscrew Gear
Enter the number of teeth on the leadscrew gear in the standard setup eg 56.
This is needed to calculate gearbox gear ratios and primary ratio of the gearbox. e.g. For the Boxford A lathe it should be 56.
Unless you have a Chinese lathe or other unusual brand you do not need the entries highlighted in green below, but MAKE SURE THEY ARE BLANK. Also check the buttons for fixed stud and leadscrew years, which in most cases should say "no". But some older Western lathes may have either the stud gear or leadscrew gear designed in such a way that they cannot be changed.
The program needs to know the gear train used for cutting a thread equal to the pitch of the leadscrew. This is required to calculate the gearbox gear ratios. For Western lathes all we usually need is the number of teeth on the stud gear and leadscrew gear (assuming that there is only an idler gear between them, and no compound gears for the standard setup.)
Finally go to the Instructions at the bottom.
Chinese lathes like the popular Grizzly models are more complicated because they may have compound gears in the standard gear train for cutting a thread the same as the leadscrew pitch. This will require two or four more entries for these extra gears in addition to the stud or spindle gear and leadscrew gear. These are highlighted in green. They are reset to zero because they must be zero for non-Chinese lathes. If your standard gear train does not use compound gears leave all four blank. If you only require one compound pair complete stdComp1 and stdComp2 but leave stdComp3 and stdComp4 blank. If your standard set has two compound pairs you will need to complete all four.
Chinese lathes often only have a 3 speed gearbox with ratios of 0.5, 1.0, 2.0. It may be simpler to set the gearbox on 1.0 for screw cutting and treat this like a lathe without a gearbox. These lathes generally have no reverse tumbler gears in the gear train and no removable stud gear. Instead there is a gear machined into the spindle and that plays the same role as the stud gear, but it cannot be changed. The number of teeth on the spindle gear should be entered as a substitute for the stud gear in the entry above.
Western lathes usually have an idler gear between the stud gear and leadscrew gear and idler wheels have no effect on the gear ratio, although they change the direction of rotation. There may be some exceptions where Western lathes do require compound gears to obtain the standard threads shown on the tables. Chinese lathes may have one idler and one compund gear, or alternatively, may have two compound gears in series in the standard gear train, and these are placed between the spindle (stud) gear and the leadscrew gear. The compound pairs of gears do affect the gear ratios and have to be taken into account when calculating gearbox ratios.
In this program the gears are assigned names as follows: The spindle gear (also called a fixed stud gear) drives compound gear stdComp1 (a driven gear), which is physically connected to compound gear stdComp2 by a keyway, and this drives compound gear stdComp3 (a driven gear), which is physically connected to compound gear stdComp4 by a key. stdComp4 drives the leadscrew gear (the final driven gear). Enter the number of teeth on each of these gears.
FYI: gear ratios are calculated at the points where gear teeth mesh with one another, using the ratio driver / driven. So with this setup we can calculate the Gear Train Ratio (stdGTR) from the number of teeth on each gear starting with the spindle or stud gear as a driver gear, as follows:
stdGTR= stud/comp2 x comp2/comp3 x comp4/LSG
where LSG is the gear on the leadscrew or gearbox input.
Compound Gear #1
Compound Gear #2
Compound Gear #3
Compound Gear #4
Changeable stud or spindle gear
Can the stud or spindle gear be removed and changed? Some Asian lathes have the stud gear machined as part of the spindle shaft, so that it cannot be changed. This is the first gear in the gear train. The stud gear entered above will be used. Similarly, the gear mounted on the gearbox input may be fixed and "unchangeable". In that case the leadscrew gear entered above will be used.
Western lathes generally have a changeable stud gear mounted, on a special shaft (stud) spinning at the same speed as the chuck spindle. eg yes
Changeable Leadscrew gear
Can the leadscrew gear (LSG) be removed and changed? eg yes
Some lathes have the leadscrew gear embedded in the gearbox housing. In that case they cannot be changed, and you should select NO, and the program will use the number of teeth entered above for the LSG.
Thank you for entering all that data. Now all you need to do is to click the PERFORM CALCULATIONS button below and then send me an email including the code shown below the following table. I can insert this code into the program. It would be helpful if you copy the URL in the address bar and send it to me by email too. Then I can add your lathe to the permanent list. Save a copy as a bookmark or favorite as well.
Meanwhile, you can use your custom gearbox immediately. When you go back to the menu the program will carry out all the calculations necessary to set up your gearbox ratios and other data.
FYI: You may notice that the numbers assigned to the columns in the table have been divided by the number on the original table where the column crosses the row that you chose, (this may be the leadscrew pitch or TPI). I call this 'normalization'. It ensures that the table of F-factors gives actual thread numbers. The 'F-factor' values are calculated by multiplying the column by the row.